Endless fabric

ABSTRACT

The invention relates to an endless belt, especially made of felt or sieve, for a machine for producing and/or upgrading a Web ( 1, 11, 21 ) of paper, paperboard, tissue or other fibers. The inventive belt has an increased adhesive power in adhesive zones ( 3, 14, 24 ) that extend opposite the marginal zones ( 4, 12 ) of the fiber web ( 1, 11, 21 ).

[0001] This application corresponds to and claims foreign prioritybenefits under 35 U.S.C. 119 (a)-(d) or (f), or 365 (b) based uponGerman patent applications No. 100 37 367.4 filed Jul. 31, 2002, and No.201 07 844.9 filed May 9, 2001, and No. 201 07 846.5 filed May 9, 2001.

[0002] The invention generally relates to an endless fabric, inparticular a felt or a screen, for a machine for the manufacture and/orconverting of a paper web, a card web, a tissue web or another fiberweb.

[0003] It relates among other things to a compressible, water absorbingand endless pressing felt for use in pressing sections for thedewatering of paper webs, card webs, tissue webs or other fiber webs aswell as to a method for the manufacture of the same, furthermore to aformer screen of a former for the forming of a sheet of a machine forthe manufacture of a paper web, a card web, a tissue web or anotherfiber web, said screen transferring the fiber web to a succeedingmachine unit and also continuing to transport the edge strips of thefiber web separated prior to the transfer of the fiber web after thetransfer of the fiber web, and finally to a drying screen of a dryingsection of a machine for the manufacture and/or converting of a paperweb, a card web, a tissue web or another fiber web which guides thefiber web and partly surrounds at least one heated rotating dryercylinder, with the fiber web coming into contact with the dryercylinder.

[0004] In particular with press nips having pressing felts arranged atboth sides of the fiber web, guide problems frequently occur after thepress nip with respect to the fiber web (after the leading away of apressing felt). This applies above all with relatively high dry contentsof the fiber web. Consequently, web edge lifting can occur, which can inturn result in crease formation, tears or even tearing-off of the fiberweb.

[0005] Previously, this has been countered by a suction of the pressingfelt in the region at risk on the side remote from the fiber web.However, this is very expensive with respect to design and energy.

[0006] The dewatering and formation of the fiber web takes place in theformer, with the fiber web being guided by at least one former screen.The former screen is permeable for air and water and usually transfersthe fiber web to a pressing felt of a succeeding pressing section forthe further dewatering of the fiber web.

[0007] The fiber web formed in the former is generally wider thannecessary, since only the homogeneously formed center part of the fiberweb is further treated in the following machine unit. The separation ofthe edge strip therefore takes place by means of a water jet prior tothe transfer of the fiber web.

[0008] For the drying of the fiber web, it is guided in dryer groups ofthe drying section, generally supported by a drying screen, via guiderolls and heated dryer cylinders, with the fiber web coming into contactwith the smooth surface of the dryer cylinder. Due to the adhesion ofthe fiber web to the dryer cylinder which thereby results, the fiber webtends to run with the dryer cylinder when the drying screen is guidedaway. This is in particular problematic with a high moisture content ofthe fiber web, i.e. at the start of the drying section.

[0009] To counteract this, the dryer groups are made very short at thestart of the drying section and tensions, that is different speeds, arebuilt up between the dryer groups. This is not only complex, it alsostrains the fiber web.

[0010] It is therefore an object of the invention, to improve theguiding of the fiber web at the pressing felt using simple means. Afurther object of the invention consists of ensuring that the edgestrips also adhere to the former screen after the transfer of the centerpart to the former screen even at high machine speeds. Finally, it isthe underlying object of the invention to counteract the adhesion of thefiber web to the dryer cylinder with means which are as simple aspossible.

[0011] These objects are generally satisfied in accordance with theinvention, in that the endless fabric in question has increased adhesionin adhesion zones which extend opposite the edge regions of the fiberweb.

[0012] In accordance with the invention, the object set with respect tothe pressing felt is satisfied in that the pressing belt has increasedadhesion in adhesion zones extending opposite the edge regions of thefiber web. This results in improved adhesion of the edge regions andthus also of the whole fiber web at the pressing felt. The adhesionzones can admittedly cause differences in quality in the edge regions ofthe fiber web, but since the edge regions are generally anyway cut offin the following machine units, this is insignificant. It is sufficientfor the achieving of good adhesion, also under the aspect of minimizingthe trimmings, for the adhesion zones of the pressing felt to each coverone edge region of the fiber web with a width between 2 up to 25 cm.

[0013] However, it is also possible per se, or in combination with theaforesaid solution, for the pressing felt to have an increased airpermeability in adhesion zones extending opposite the edge regions ofthe fiber web. The efficiency of suction devices on the edge regions ofthe fiber web improves due to the reduced flow resistance, with thesuction devices being arranged, for example in the form of suction boxesor suction rolls, on the side of the pressing felt opposite the fiberweb. With respect to design, the pressing felt can be designed like ascreen and/or have larger pores.

[0014] A possibility of increasing the adhesion of the pressing feltlies in that fact that the pressing felt is coated or soaked with apolymer, preferably polyurethane or polyamide, in the adhesion zone atleast on the side contacting the fiber web, with it being of advantagewith respect to the manufacture for the adhesion zone to be treated witha liquid polymer and to be treated again, in particular ground and/orimprinted after the hardening thereof.

[0015] Another solution for the improvement of the adhesion lies in thefact that the pressing felt has finer mat fibers in the adhesion zone,at least at the surface contacting the fiber web, than between theadhesion zones, the diameter of said mat fibers preferably being smallerthan 27 micrometers and/or having chemically treated mat fibers.Complementary to this, or as an independent variant, it is, however,also possible for the pressing felt to have a larger number of matfibers in the adhesion zone, at least at the surface contacting thefiber web, than at the surface between the adhesion zones.

[0016] In all solutions, however, the thickness of the pressing felt inthe adhesion zone in the loaded state should differ from the thicknessbetween the adhesion zones by a maximum of 1 mm, preferably a maximum of0.5 mm. This restricts the effects on the quality of the fiber web, inparticular on the edge regions. In this connection, it is also ofadvantage for the compressibility of the pressing felt in the directionof thickness and/or the longitudinal extent of the pressing felt undertension to be as constant as possible over the width of the pressingfelt.

[0017] In accordance with the invention, the object set with respect tothe former screen is correspondingly satisfied in that the former screenhas increased adhesion in adhesion zones which extend opposite the edgeregions of the fiber web. This results in improved adhesion of the edgestrips to the former screen such that there is no scrap flying.

[0018] A possibility of increasing the adhesion consists of the factthat the former screen has a lower air permeability in the adhesionzones than in the main region lying therebetween. The former screenshould preferably even be made impermeable to air in the adhesion zones.This makes the rear ventilation, and thus the separation of the edgezones, more difficult.

[0019] For this purpose, the former screen should preferably be filledwith a polymer, preferably polyurethane, in the adhesion zones.

[0020] The adhesion can also be increased in that the former screen hasa smooth surface in the adhesion zones at the side facing the fiber web.Due to the good adhesion, the adhesion zones do not have to cover thewhole width of the edge strips. Preferably less than 60%, in particularless than 40%, of the width of the edge strips is usually sufficient.

[0021] In the use of such a former screen in a former, at least onescraper and/or water nozzle and/or air nozzle should be associated withthe adhesion zones after the transfer of the fiber web for the removalof the edge strips from the adhesion zones.

[0022] In cases in which the former is formed by two former screenswhich are usually arranged over one another and between which the fiberweb extends, only one former screen, preferably the one which transfersthe fiber web to the next machine unit, should have adhesion zones. Thisis generally the lower former screen.

[0023] In accordance with the invention, the object set with respect tothe dryer screen is satisfied in that the dryer screen has increasedadhesion in adhesion zones extending opposite the edge regions, with thefact being taken into account that in particular the edge regions of thefiber web adhere more pronouncedly to the dryer cylinder. It istherefore sufficient to arrange adhesion zones opposite the edges of thefiber web.

[0024] The adhesion zones of the dryer screen should each cover an edgeregion of the fiber web with a width from 300 to 100 mm.

[0025] A possibility of increasing the adhesion consists of the factthat the dryer screen has a smooth surface in the adhesion zones at theside facing the fiber web. It is further also possible per se, or incombination with the smooth surface, for the dryer screen to have alower air permeability in the adhesion zones than in the main regionlying therebetween. The adhesion zones should preferably even be madeimpermeable to air.

[0026] This design of the adhesion zones in particular becomes possiblein that the dryer screen is filled with a polymer, preferablypolyurethane, in the adhesion zones.

[0027] The impairment of the air permeability in the adhesion zonesobstructs a rear ventilation and thus increases the adhesion of thefiber web to the dryer screen. On the other hand, however, this impairsthe steaming out, and thus the drying, of the fiber webs in the edgeregions. However, this can be accepted in the edge regions since theseare anyway later cut off and/or usually anyway tend to overdrying.

[0028] Dryer screens designed in this manner should in particular beused in dryer groups of the drying section in which only one side of thefiber web comes into contact with heated dryer cylinders. This issubstantially due to the fact that the fiber web does not have to betransferred between dryer screens in these dryer groups.

[0029] The invention should be explained in more detail below withreference to various embodiments and to the drawing, in which are shown:

[0030]FIG. 1 a cross-section through the edge of a pressing felt;

[0031]FIG. 2 a schematic cross-section through an end region of aformer;

[0032]FIG. 3 a cross-section through a former screen with fiber web; and

[0033]FIG. 4 a cross section through the edge of a dryer screen.

[0034] Reference is made in the following to FIG. 1, in which across-section through the edge of a pressing felt 2 is shown.

[0035] In particular in pressing sections of paper making machines forthe dewatering of paper webs using two long press nips, through whichone respective, usually separate, endlessly circulating pressing felt 2extends on both sides of the fiber web 1, problems result in the guidingof the fiber web 1 above all at high speeds. The fiber web 1 reaches arelatively high drying content after only the first press nip, whichreduces the adhesion to the pressing felt 2. This naturally only becomesa problem when the pressing felt 2 is guided off at the other side ofthe fiber web 1. The low adhesion of the fiber web 1 to the pressingfelt 2 often results in the lifting off of the web edges of the fiberweb 1. This results in turn in web flutter or web tears.

[0036] To solve this problem, a pressing felt 2 is used in addition to asuction of the leading pressing felt 2, or above all on its own, whichhas increased adhesion in adhesion zones 3 extending opposite the edgeregions 4 of the fiber web 1. Since this is usually associated with achanged surface structure in the adhesion zone 3 of the pressing felt 2,impairments in the quality of the fiber web 1 in the edge region 4cannot be precluded. It is, however, sufficient for a good adhesion ofthe fiber web 1 to the pressing felt 2 for the adhesion zones 3 of thepressing felt 2 to each cover an edge region 4 of the fiber web 1 with awidth of approximately 10 to 15 cm. Since these edge regions 4 are cutoff in succeeding units of the paper making machine, at the latest onthe wrapping up, this impairment of quality is without consequences.

[0037] To increase the adhesion, the surface of the pressing felt 2coming into contact with the fiber web 1 in the adhesion zone 3, whichextends here up to the end of the pressing felt 2, is coated withpolyurethane, with the polyurethane also penetrating into the pressingfelt 2.

[0038] After the thermal or chemical hardening of the polyurethane, thegrinding off of elevations of this coating as well as a roughening ofthe surface of the coating takes place by means of an imprinting roll.Too smooth an adhesion zone 3 could have the consequence of too strongan adhesion of the fiber web 1, which results in difficulties in thehanding over of the fiber web 1.

[0039] Since this coating with a polymer 5 results in a thickening ofthe adhesion zones 3 of the pressing felt 2, care must be taken, inparticular in the subsequent treatment, that the thickness of thepressing felt 2 in the adhesion zone 3 in the unloaded state is at amaximum 0.5 mm larger than between the adhesion zones 3. It mustmoreover be observed in the polymer 5 and in the penetration of thepressing felt 2 by this polymer 5 that the compressibility of thepressing felt 2 in the thickness direction and/or the longitudinalextent of the pressing felt 2 under tension is as constant as possibleover the width of the pressing felt 2.

[0040] The coating with the polymer 5 can result in the fact that thepressing felts 2 become impermeable to water in the adhesion zone 3 andcan no longer absorb any water. However, due to the following trimming,these wetter, narrow edge regions 4 also do not bring along anydisadvantages with them.

[0041] Instead of the coating with the polymer 5, the adhesion in theadhesion zone 3 can also be improved in that the pressing felt 2 in theadhesion zone 3 has finer mat fibers at least at the surface contactingthe fiber web 1 than between the adhesion zones 3, whose diameter ispreferably smaller than 27 μm, and/or has chemically treated mat fibers,and/or the pressing felt 2 in the adhesion zone 3 has a larger number ofmat fibers at least at the surface contacting the fiber web 1 than atthe surface between the adhesion zones 3. This also results in a changedsurface structure in the adhesion zone 3 of the pressing felt 2.

[0042] Reference is made in the following to FIGS. 2 and 3 in which aschematic cross-section through an end region of a former or a partsection through a former screen 13 with a fiber web 11 is shown.

[0043] The former of a paper making machine for the dewatering andforming of the fiber web 11, that is here specifically of the paper web,is formed by two endlessly circulating former screens 13, 18 which arearranged over one another and between which the fiber web 11 lies.

[0044] The former screens 13, 18 guided via guide rolls 13, 18 areseparated from one another at the end of the former, with the fiber web11 running along with the lower former screen 13.

[0045] The cutting off of the edge strips 12 from the homogeneous partof the fiber web 11 subsequently takes place via water jet nozzles 22.Subsequently, the fiber web 11 is taken over by a pressing felt 19 ofthe following pressing section wrapping around a guide roll 20 withsuction for the further dewatering.

[0046] The lower former screen 13 has adhesion zones 14 of increasedadhesion opposite the edge strips 12. For this purpose, the adhesionzones 14 of the former screen 13 are filled with polyurethane. While themain region 15 of the former screen 13 is permeable to air for thedewatering of the fiber web 11, the adhesion zones 14 are impermeable toair. In addition, the surface of the adhesion zones 14 facing the edgestrips 12 is smooth. Both measures result in the fact that the edgestrips 12 also adhere securely to the former screen 13 after the handingover of the fiber web 11.

[0047] The release of the edge strips 12 from the former screen 13 bymeans of a respective scraper 16 and the guiding away into the pulperonly takes place later. A cleaning of the former screen 13, inparticular of the adhesion zones 14, then takes place via water nozzles17, with contaminants and the splashing water being taken up by asuction bell 23.

[0048] Reference is made in the following to FIG. 4 in which across-section through the edge of a dryer screen 22 is shown.

[0049] For the drying in the single-row dryer group of a drying section,the fiber web 21, guided by the dryer screen 22, runs alternately overguide rolls and heated rotating dryer cylinders 23, with it coming intocontact with the dryer cylinders 23.

[0050] To be able to guide off the fiber web 21 relatively simply andreliably from the dryer cylinder 23 after the part wrapping around, thedryer screen 2 has increased adhesion in adhesion zones 24 extendingopposite the edge regions of the fiber web 21.

[0051] For this purpose, the dryer screen 22 is filled with polyurethanein the adhesion zones 24. The adhesion zones 24 are not only impermeableto air, but are also smooth opposite the fiber web 21.

[0052] Since in particular the edge regions of the fiber web 21 tend toincreased adhesion to the smooth dryer cylinder 23, it is sufficient forthe adhesion zones 24 each to cover an edge region of the fiber web 21with a width between 30 and 100 mm.

REFERENCE NUMERAL LIST

[0053]1 fiber web

[0054]2 pressing felt

[0055]3 adhesion zone

[0056]4 edge zone

[0057]5 polymer

[0058]11 fiber web

[0059]12 edge strip

[0060]13 former screen

[0061]14 adhesion zone

[0062]15 main region

[0063]16 scraper

[0064]17 water nozzles

[0065]18 former screen

[0066]19 pressing felt

[0067]20 guide roll with suction

[0068]21 guide roll

[0069]22 water jet nozzle

[0070]23 suction bell

1. An endless fabric, in particular a felt (2) or a screen (13, 22), fora machine for the manufacture and/or converting of a paper web, a cardweb, a tissue web or another fiber web (1, 11, 21), characterized inthat the endless fabric (2, 13, 22) has increased adhesion in adhesionzones (3, 14, 24) extending opposite the edge regions (4, 12) of thefiber web (1, 11, 21).
 2. An endless fabric in accordance with claim 1,characterized in that it is formed by a compressible, water absorbingand endless pressing felt (2) for use in pressing sections for thedewatering of paper webs, card webs, tissue webs or other fiber webs(1).
 3. An endless fabric (2) in accordance with claim 2, characterizedin that the adhesion zones (3) of the pressing felt (2) each cover anedge region (4) of the fiber web (1) with a width between 2-25 cm.
 4. Anendless fabric (2) in accordance with claim 2, characterized in that thepressing felt (2) is coated with a polymer (5), preferably polyamide, inthe adhesion zone (3) at least on the side contacting the fiber web (1).5. A method for the manufacture of the endless fabric or pressing felt(2) in accordance with claim 4, characterized in that the adhesion zoneis treated with a liquid polymer (5), and treated again, in particularground and/or imprinted, after the hardening thereof.
 6. An endlessfabric in accordance with claim 2, characterized in that the pressingfelt (2) has finer mat fibers in the adhesion zone (3), at least at thesurface contacting the fiber web (1), than between the adhesion zones(3), whose diameter is preferably smaller than 27 μm and/or haschemically treated mat fibers.
 7. An endless fabric (2) in accordancewith claim 2, characterized in that the pressing felt (2) has a largernumber of mat fibers in the adhesion zone (3), at least at the surfacecontacting the fiber web (1), than at the surface between the adhesionzones (3).
 8. An endless fabric (2) in accordance with claim 2,characterized in that the thickness of the pressing felt (2) in theadhesion zone (3) deviates in the loaded state by a maximum of 1 mm,preferably a maximum of 0.5 mm, from the thickness between the adhesionzones (3).
 9. An endless fabric in accordance with claim 2,characterized in that the compressibility of the pressing felt (2) inthe thickness direction and/or the longitudinal extent of the pressingfelt (2) under tension is as constant as possible over the width of thepressing felt (2).
 10. An endless fabric, in particular a felt (2) or ascreen (13, 22) for a machine for the manufacture and/or converting of apaper web, a card web, a tissue web or another fiber web (1, 11, 21), inparticular in accordance with claim 1, characterized in that it isformed by a compressible, water absorbing and endless pressing felt (2)for use in pressing sections for the dewatering of paper webs, cardwebs, tissue webs or other fiber webs (1); and in that the pressing felt(2) has an increased permeability for air in adhesion zones (3)extending opposite the edge regions (4) of the fiber web (1).
 11. Anendless fabric in accordance with claim 1, characterized in that it isformed by a former screen (13) of a former for the forming of a sheet ofa machine for the manufacture of a paper web, of a card web, of a tissueweb or of another fiber web (11), the screen transferring the fiber web(11) to a succeeding machine unit (11) and also continuing to guide theedge strips (12) of the fiber web (11) cut off prior to the transfer ofthe fiber web (11) after the transfer of the fiber web (11).
 12. Anendless fabric (13) in accordance with claim 11, characterized in thatthe former screen (13) has a lower permeability in the adhesion zones(14) than in the main region (15) therebetween.
 13. An endless fabric(13) in accordance with claim 11, characterized in that the formerscreen (13) is impermeable to air in the adhesion zones (14).
 14. Anendless fabric (13) in accordance with claim 11, characterized in thatthe former screen (13) is filled with a polymer in the adhesion zone(14).
 15. An endless fabric (13) in accordance with claim 11,characterized in that the former screen (13) has a smooth surface in theadhesion zones (14) on the side facing the fiber web (11).
 16. A formercomprising a former screen (13) in accordance with claim 11,characterized in that a scraper (16) and/or water nozzles (17) and/orair nozzles is/are associated with the adhesion zones (14) of the formerscreen (13) after the transfer of the fiber web (11) for the removal ofthe edge strips (12) from the adhesion zones (14).
 17. A former inaccordance with claim 16, characterized in that the former is formed bytwo former screens (13, 18) arranged over one another, between which thefiber web (11) extends, with preferably only the former screen (13)which transfers the fiber web (11) to the next machine unit havingadhesion zones (14).
 18. A former in accordance with claim 11,characterized in that the adhesion zones (14) only cover part of theedge strips (12), preferably less than 60%, in particular less than 40%,of the width of the edge strip (12).
 19. An endless fabric in accordancewith claim 1, characterized in that it is formed by a dryer screen (22)of a drying section of a machine for the manufacture and/or convertingof a paper web, of a card web, of a tissue web, or of another fiber web(21), the screen guiding the fiber web (21) and at least partly wrappingaround a heated, rotating dryer cylinder (23), with the fiber web (21)coming into contact with the dryer cylinder (23).
 20. An endless fabric(22) in accordance with claim 19, characterized in that the adhesionzones (24) of the dryer screen (22) each cover an edge region of thefiber web (21) with a width from 30 to 100 mm.
 21. An endless fabric (2)in accordance with claim 19, characterized in that the dryer screen (22)is filled with a polymer in the adhesion zones (24).
 22. An endlessfabric (22) in accordance with claim 19, characterized in that the dryerscreen (22) has a lower air permeability in the adhesion zones (24) thanin the main region (25) therebetween.
 23. An endless fabric (2) inaccordance with claim 19, characterized in that the dryer screen (22) isimpermeable to air in the adhesion zones (24).
 24. An endless fabric(22) in accordance with claim 19, characterized in that the dryer screen(22) has a smooth surface in the adhesion zones (24) on the side facingthe fiber web (21).
 25. Use of the endless fabric or of the dryer screen(22) made in accordance with claim 19 in dryer groups of the dryersection in which only one side of the fiber web (21) comes into contactwith heated dryer cylinders (23).